Polymers comprising ethylene and propylene are well known in the art and are used in many applications. Such polymers include random, block, and alternating copolymers prepared from a variety of catalysts and catalyst systems and in a variety of polymerization processes.
Ethylene/α-olefin block interpolymers are described in PCT Publication No. WO2009/012216. The polymers are said to be prepared using two catalysts having differing comonomer incorporation indices and a chain shuttling agent. The polymers are said to have melting temperatures as high as 100° C., with reported melting temperatures for exemplary polymers as high as about 74° C. Block interpolymers are also described in PCT Publication Nos. WO2009/012214, WO2009/012152, and WO2009/012153.
It would be desirable to produce blocky copolymers of ethylene and propylene having similar or superior properties to those previously described but which can be produced without the added complexity and cost of a chain shuttling agent. The present invention addresses this by providing copolymers comprising ethylene and propylene and having semicrystalline ethylene sequences and amorphous or low crystallinity propylene sequences. The polymers are preferably prepared using metallocene-based catalyst systems but without the use of a chain shuttling agent. The polymers have higher melting temperatures than previously known random copolymers or blocky copolymers having similar comonomer contents and which are prepared with chain shuttling agents.